1. Field of the Invention
The present invention relates to a multi-optical axis photoelectric sensor which detects entry into a predetermined area by means of a plurality of optical axes.
2. Description of the Background Art
In order to ensure safety of a worker from a source of danger such as a presser and a bender, a so-called multi-optical axis photoelectric sensor has hitherto been used as a sensor for detecting a person and an object entering a predetermined area near the source of danger. The multi-optical axis photoelectric sensor has a phototransmitter in which a large number of light projecting elements are arranged in line, and a photoreceiver in which the same number of light receiving elements as the number of the light projecting elements are arranged in line. The phototransmitter and photoreceiver are arranged as opposed to each other, to form a plurality of optical axial columns that partition a dangerous region. The formed plurality of optical axial columns are called a light curtain, and when a light interrupting object enters this light curtain, a safety signal for forcibly stopping an operation of the source of danger is outputted from the light curtain to a control panel that controls the operation of the source of danger. It is thereby possible to ensure the safety of the worker.
Generally, the phototransmitters and the photoreceivers are each connected to the control panel through one cable. Further, for synchronization of timing for light projection/reception between the phototransmitter and the photoreceiver, the phototransmitter and the photoreceiver are connected to each other inside the control panel, for example, through a data communication line (e.g., Japanese Unexamined Patent Publication No. 2008-180653). In a multi-optical axis photoelectric sensor disclosed in Japanese Unexamined Patent Publication No. 2008-180653, a phototransmitter and a photoreceiver are connected through a communication line or a signal line L1.
However, in wiring in which the phototransmitter and the photoreceiver are connected with the control panel through different cables, two cables need to be separately routed to the control panel, and the routing of the wires is thus laborious and may cause deterioration in workability of wiring work.
In this respect, by use of a T-branch connector that combines two cables into one cable, the cables connecting the phototransmitter and the photoreceiver with the control panel may be made into one cable. Specifically, the cable extending from the phototransmitter and the cable extending from the photoreceiver are connected to the T-branch connector to be combined into one cable, and the T-branch connector and the control panel are connected to each other through the one cable. Hence the number of cables connected to the control panel becomes one, thereby making it possible to prevent the foregoing deterioration in workability. However, when it comes to combining cables into one cable by use of the T-branch connector, wiring cost may increase due to an increase in number of components, and the work efficiency may deteriorate due to the fact that the T-branch connector needs to be separately prepared.